The process for issuing recommendations included review of recent published literature including standard indexed journals, vaccine trials, recommendations of reputed international bodies like Advisory Committee on Immunization Practices, Center for Disease Control and Prevention (CDC), USA, World Health Organization (WHO) and unpublished data from vaccine manufacturers. Data generated by studies done in India was specifically looked at and available local information was given preference. The summary of the key updates of ACVIP 2020-2021 recommendations is given in Box I.

The ACVIP-IAP recommendations for the year 2020-21 are being given in Table I and Fig. 1. The recommendations about the newly introduced vaccines are summarized in Box II and vaccines for high risk children are summarized in Box III.

Fig. 1 ACVIP recommendations 2020-21.

(a) To be given within 24 h after birth. When this is missed, it can be administered at first contact with health facility; (b) An extra dose of Hepatitis B vaccine is permitted as part of a combination vaccine when use of this combination vaccine is necessary; (c) IPV can be given as part of a combination vaccine; (d) 3rd dose of Rota vaccine is not necessary for RV1; (e) Influenza vaccine should be started after 6 mo of age, 2 doses 4 wks apart, usually in the pre-monsoon period. At other times of the year, the most recent available strain should be used. Annual influenza vaccination should be continued, for all, till 5 y of age; after the age of 5y, this vaccine is recommended in the high-risk group only; (f) Single dose is to be given for the live attenuated Hepatitis A vaccine. The inactivated vaccine needs two doses; (g) 2nd dose of Varicella vaccine should be given 3-6 mo of age after dose 1. However, it can be administered anytime 3 mo after dose 1 or at 4-6 y; (h) Tdap should not be administered as the second booster of DPT at 4-6 y. For delayed 2nd booster, Tdap can be given after 7 y of age. A dose of Tdap is necessary at 10-12 y, irrespective of previous Tdap administration. If Tdap is unavailable/unaffordable, it can be substituted with Td; (i) Before 14 completed years, HPV vaccines are recommended as a 2-dose schedule, 6 mo apart; (j) From 15th y onwards and the immunocompromised subjects at all ages, HPV vaccines are recommended as a 3-dose schedule, 0-1-6 (HPV2) or 0-2-6 (HPV4); (k) Menactra is approved in a 2-dose schedule between 9-23 mo. Minimum interval between two doses should be 3 mo. Menveo is recommended as a single dose schedule after 2 y of age.

The last case of wild polio virus (WPV) in India was reported on 13 January, 2011 and on 27 March, 2014, India along with the rest of Southeast Asia was declared polio-free [1]. It needs to be emphasized that until worldwide polio eradication is achieved, cases of imported WPV from endemic neighboring countries or cases of circulating vaccine derived poliovirus (cVDPV), remains a real threat unless population immunity is maintained by vaccinating children adequately in their early years of life. Outbreaks of cVDPVs have occurred in countries which have been polio free for several years [2]. In the absence of inapparent infection, universal vaccination of infants and children is the only way to establish and maintain population immunity against polio. In 2018, the ACVIP had recommended an all IPV schedule at 6-10-14 weeks followed by an IPV booster at 15-18 months, and the recommendation for the OPV booster at 4-6 years was dropped [3]. A birth dose of OPV continues to be recommended.

IPV is immunogenic in an EPI schedule (6-10-14 weeks), but the titers achieved and the seroconversion rates are reported to be lower, compared with vaccination of infants at older ages (2-4-6 months) [4]. Studies examining the long-term persistence of antibodies following IPV vaccination, have shown persistence of antibodies only up to the school-entry age, with the highest titers observed with the 3+1 schedule [4], as all IPV using countries recommend a school age booster [5]. A pre-school booster resulted in SPR rising to 100% for all 3 serotypes and GMTs rising 32-fold to 55-fold for the 3 serotypes [6,7]. Following a pre-school booster, almost 100% SPR and high antibody titers persist for at least 5 years [8].

In April 2016, a synchronous global switch was implemented from trivalent OPV (tOPV) to bivalent OPV (bOPV) in routine immunization programs. Simul-taneously, IPV was introduced in the routine Immunization in all OPV-only using countries. Introduction of IPV was a risk mitigation strategy to overcome the risk associated with this switch. The switch was preceded by high quality SIAs with tOPV, to raise population immunity against type 2 PV [13]. Modelling studies done prior to the switch suggested that the risk of cVDPV would not last beyond a year and a half of the switch [14].

With a massive surge in requirements for IPV, a shortage resulted. According to the data published by the WHO, global coverage with one dose of IPV was about 50% in 2016, 60% in 2017, and only 72% in 2018 [15]. Thus, population immunity against PV type 2 has decreased, with resultant increase in cVDPV cases/outbreaks [16,17]. In 2017, there were two countries with cVDPV2 outbreaks with 96 cases; whereas, as of 13 October, 2020, worldwide there were 449 cases of cVDPV2 [18]. This data suggests that India is not free from the risks of cVDPV. In fact, India comes under the category of countries at high risk for cVDPV. Moreover, India has a long border with Pakistan, a country which is still endemic for WPW type 1. There is an imperative need to maintain population immunity against type 2 PV, which can only be achieved by administering IPV either in the IAP schedule or 2 doses of fractional dose intradermal IPV at 6 weeks and 14 weeks or a single dose of full-dose intramuscular IPV at 14 weeks. No child born after the switch should be left unprotected against type 2 PV.

Since the 1970s, when whole virion vaccines were in use, the standard-dose of IIVs in children less than 3 years of age has been 7.5 mcg per antigen, which is half the dose, given to older children and adults. As higher dose increased the reactogenicity, the lower dose was adopted to reduce reactogenicity and febrile convulsions observed with the whole virus vaccines that were in use at that time [19]. However, the immune response in young children was very variable, especially against the B strains in the vaccine. This was particularly significant in children younger than 3 years of age, who were vaccine-naïve [20]. Higher dose of 0.5 mL (15µg) in the 6-23 months age group is expected to result in higher levels of post vaccination HI antibody titer, which may result in increased efficacy [21]. Since, the complications of influenza are much higher in infants, studies were done to evaluate the safety, immunogenicity and superiority of full dose (0.5 ml; 15 µg) in the age group of 6-35 months to have uniform dosage recommendations in all age groups.

Studies have generally shown comparable reactogenicity and non-inferior immunogenicity with the full dose, in comparison with the half dose, in children 6-35 months of age [22-25]. Statistically superior immunogenicity was seen only in infants between 6-11 months of age, for H3N2 and B/Yamagata and not for H1N1 [25]. Superior GMTs were demonstrated against both vaccine B strains in children 6-17 months of age and unprimed children 6-35 months of age [24].

In children 6-35 months of age, the quadrivalent vaccine in a dose of 0.5 ml, demonstrated an efficacy of 63% (97·5% CI 52-72) against moderate-severe influenza, in a season when there was a 68% mismatch between the vaccine strains and the strains isolated in the study [25].

Several countries including USA, Finland, Australia, UK, New Zealand and Canada have adopted a uniform dosage schedule for all age groups.

The timing of the second dose would depend on the relative contributions of primary and secondary vaccine failure to the incidence of breakthrough varicella. Primary vaccine failure could be defined as the failure to seroconvert or the failure to mount a protective immune response after vaccination despite seroconversion, whereas secondary vaccine failure is the gradual waning of immunity over time. Primary vaccine failure will favor an early second dose (few months after dose 1), whereas secondary vaccine failure will favor a delayed second dose (few years after dose 1).

Studies examining the immunological response to the second dose given after 6 weeks and given after 4-5 years have shown that the SPR (>5 U/mL by gpELIZA) are similar with both schedules, while the GMTs are higher with the longer interval schedule. However, the mean Stimulation Index (SI), which is a marker of the CMI is superior when the second dose is administered at 4-5 years [28,29]. Increases of GMTs by > 10-fold is observed following the second dose, irrespective of the interval between doses [30,31]. This is not seen with other viral vaccines. Such large increases suggest an inadequate priming and that the second dose is for completing the immune response initiated by the first dose.

Persistence of antibody in children after 1 dose of varicella vaccine has been demonstrated in both short-term and long-term follow-up studies [32-34], for periods as long as 9-20 years, with titers rising during the period of follow-up [32,34], indicating an absence of waning of antibody titers with time especially when there are occasions for natural boosting, thus suggesting a primary vaccine failure rather than waning immunity.

The highest incidence rate of breakthrough varicella was seen in the first 4-5 years after vaccination [35]. Vaccine effectiveness dropped from 97% in the first year post-vaccination to 86% in the second year and then remained stable till 8 years [36]. In a study from China, effectiveness was also shown to drop after the first year and then remain stable over the next 5 years [37]. These patterns are seen in primary vaccine failure, rather than waning immunity.

A single retrospective study has demonstrated an increasing incidence and severity over 10 years [38]. Some outbreak studies, which do not represent the entire population, have suggested waning immunity as a cause of vaccine failure [39].

Globally, as of end 2018, about 36 countries had included the varicella vaccine in their NIPs, about 23 have introduced a 2-dose schedule [40]. Approximately half of these 23 have preferred the shorter interval between doses.

Generally, there is more robust evidence for a primary vaccine failure following 1 dose of varicella vaccine and very limited evidence for secondary vaccine failure. A short interval between 2 doses of the varicella vaccine might be preferable to reduce breakthrough varicella, especially in countries with poor coverage and where the wild-type virus circulates predominantly. In India, in the bigger cities, 2-3 years is the usual entry age for pre-school. This may result in breakthrough varicella before the receipt of a delayed second dose. In India, varicella vaccine is not in the NIP and is recommended only by the IAP and the overall uptake is low and exposure to varicella following 1 dose may give rise to breakthrough varicella. Since the aim of varicella vaccination, in office practice, is the best possible protection for the individual child, an earlier second dose will be beneficial over a delayed second dose.

The newly introduced vaccine products are detailed below and the ACVIP recommendations for these are given in Box II.

The quadrivalent conjugate meningococcal vaccine, Menveo (Glaxo SmithKline) has been licensed by the Drug Controller General of India (DCGI). Menveo contains N. meningitidis serogroup A, C, Y, and W-135 oligosaccharides conjugated individually to Corynebac-terium diphtheriae CRM197 protein. Each dose of vaccine contains 10 µg MenA oligosaccharide; 5 µg of each of MenC, MenY, and MenW- 135 oligosaccharides; and 32.7 to 64.1 µg of CRM197 protein [41].

In the Indian licensure study, 72%, 95%, 94%, and 90% of subjects achieved a post-vaccination hSBA >8, for serogroups A, C, W, and Y, respectively, which were similar across all the 3 age groups [4]. Post-vaccination GMTs showed increases of 17-fold against serogroup A, 42-fold against serogroup C, 7-fold against serogroup W, and 15-fold against serogroup Y, compared to pre-vaccination GMTs. Post-vaccination GMTs were generally somewhat higher with increasing age. The vaccine was well tolerated with no safety concerns [44]. This vaccine is recommended for use only in special situations, as published before [45].

Typhibev (Biological E vaccines) is a typhoid conjugate vaccine where the source of the Vi antigen is C. frenundii, which is in conformity with WHO specifications. Each dose of 0.5 ml contains Typhoid Vi Polysaccharide (produced from C. Freundii sensu lato 3056): 25 µg conjugated to 16.7 µg to 100 µg of CRM197 [46].

A multicentric phase II/III study showed that seroconversion (anti-Vi IgG >2 ug/ml) was obtained in 99% subjects (95%CI: 97.06, 99.79) in Typhibev compared to 99.4% in comparator group Typbar-TCV (Bharat Biolech India Limited). Non inferiority was established with comparator TCV. Anti Vi IgG >4.3 ug/ml (criteria defined for having sustained protection for at least 4 years) also fulfilled predefined non inferiority criteria. The side effects profile was comparable with the comparator vaccine [47].

Typhibev was licensed for use in India by DCGI in February, 2020; approved for those aged older than 6 months to 45 years, to be given in 0.5 mL single dose, intramuscular injection [46].

In the 2018-19 recommendations, the ACVIP, strongly endorsed the use of monoclonal antibodies (mAbs) for rabies post-exposure prophylaxis (PEP) [3,48]. Twinrab (Zydus Vaxxicare) is the second rabies mAb to receive DCGI approval. Twinrab is a combination of two murine anti-rabies mAb, docaravimab (62-71-3) and miromavimab (M777-16-3). The two mAbs individually bind to and neutralize both rabies and rabies-like virus strains isolated from canine, human, and bovine sources, preventing their entry into the neighboring cells [49].

In a phase 3, randomized study, comparing anti-rabies monoclonal antibody cocktail (Twinrab) against Human Rabies Immunoglobulin (HRIG), the GMTs of the anti-bodies induced with Twinrab were shown to be non-inferior to the antibodies induced with HRIG, with no statistically significant difference in the two groups and a similar adverse effect profile was seen in the two groups [50].

The recommended dose of Twinrab is 40 IU/kg of body weight. Twinrab is indicated for post exposure prophylaxis in individuals with suspected rabies exposure. Twinrab must always be used in combination with rabies vaccine as part of post-exposure prophylaxis in line with the recommendation of WHO [3,48].

Pneumosil (Previously SIIPL-PCV) (Serum Institute of India Pvt Ltd Pneumococcal Conjugate Vaccine) is a pneumococcal polysaccharide conjugate vaccine that has been pre-qualified for use by WHO on 18 December, 2019 [53]. This is the third pre-qualified PCV vaccine after Prevenar-13 (Pfizer) and Synflorix (GSK vaccines).

Pneumosil is a pneumococcal polysaccharide conjugate vaccine containing saccharides of the capsular antigens of Streptococcus pneumoniae serotypes 1, 5, 6A, 6B, 7F, 9V, 14, 19A, 19F, and 23F, conjugated using CDAP (1-cyano-4-dimethylamino pyridinium tetrafluo-roborate chemistry) and chemically activated. Each dose of 0.5 ml vaccine contains 2 µg each of serotypes 1, 5, 9V, 14, 19A, 19F, 23F, 7F, 6A and 4 µg of serotype 6B conjugated to non-toxic diphtheria CRM197 carrier protein: 19-48 mcg [53]. It is available as a ready to use vial containing vaccine in liquid form with a vaccine vial monitor [54].

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