Učinkovitost cepiv proti Covid: Povzetek rezultatov študij in dejanskih podatkov

Ker velika večina ljudi ne bere strokovnih, kaj šele znanstvenih, analiz glede učinkovitosti cepiv proti Covid, v nadaljevanju podajam kratek povzetek glavnih rezultatov na podlagi dosedanjih študij ter na podlagi dejanskih podatkov na celotni populaciji. Prvi je pregledni graf s povzetkom glavnih učinkov po posameznih cepivih, kot je bil v petek objavljen v The Economistu. Kot vidite, sta na podlagi povprečja različnih študij, najbolj učinkoviti cepivi Moderna in Pfizer, ki naj bi več kot 95-odstotno varovala pred hujšim potekomi bolezni (hospitalizacijo), ter med 90 in 95-odstotno pred okužbo. Učinkovitost AstaZenece je nekaj nižja, razpršenost ocen učinkovitosti pa precej višja, glavne ocene učinkovitosti pa se gibljejo v razponu med 65 in 95-odstotno zaščito pred hospitalizacijo (centralna ocena je nekaj več od 90-odstotne zaščite). Cepivi Johnson & Johnson in Sputnik naj bi bili za rang manj učinkoviti (okrog 80-odstotno), kitajski Sinovac pa še za rang manj (okrog 60-odstotno, vendar z zelo velikim intervalom zaupanja ocen).

Covid vaccination effectiveness_21112021

Drugi vir je publikacija britanske vladne agencije UK Health Security Agency »COVID-19 vaccine surveillance report (week 45)«, na podlagi znanih rezultatov po 45. tednu letos. Prednost te publikacije je, da so podatki večinoma zbrani na podlagi celotne britanske populacije in da prikazujejo učinkovitost cepiv v tednih po cepljenju. Prvi povzetek je v spodnji tabeli, ocene so dokaj podobne kot v zgornji sliki (sicer je ta študija eden izmed virov za zgornjo sliko).

Covid vaccination effectiveness_21112021_UK HSA

Glede trajanja zaščite po cepljenju tudi podatki za Britanijo potrjujejo, da se zaščita pred okužbo in simptomatsko boleznijo sčasoma zmanjšuje. Ugotovljeno je, da se zaščita po 2 odmerkih pred okužbo zmanjša po 15+ tednih od drugega odmerka (na približno 45 do 50 odstotkov pri cepivu AstraZeneca in 70 do 75 odstotkov pri cepivu Pfizer-BioNTech in Moderna). Vendar pa zaščita pred hujšim potekomi bolezni (hospitalizacijo) in umrljivostjo v večini skupin ostaja visoka vsaj 5 mesecev po drugem odmerku (približno 80 do 90 odstotkov pri cepivu AstraZeneca in 90 do 95 odstotkov pri cepivu Pfizer-BioNTech in Moderna).

Iz tega sledi, da je priporočljiv tretji, poživitveni odmerek, ki naj bi glede na podatke iz Izraela povišal zaščito celo nad raven po drugem odmerku ter jo podaljšal vsaj na 9 do 10 mesecev.

Spodaj je kratek izsek ključnih ugotovitev iz britanske publikacije.

Vaccine effectiveness is estimated by comparing rates of disease in vaccinated individuals to rates in unvaccinated individuals. Below we outline the latest real-world evidence on vaccine effectiveness from studies in UK populations. We focus on data related to the Delta variant which is currently dominant in the UK. The findings are also summarised in Table 1.

Effectiveness against symptomatic disease

Vaccine effectiveness against symptomatic COVID-19 has been assessed in England based on community testing data linked to vaccination data from the National Immunisation Management System (NIMS), cohort studies such as the COVID Infection Survey and GP electronic health record data. After 2 doses, observed vaccine effectiveness against symptomatic disease with the Delta variant reaches approximately 65% to 70% with AstraZeneca Vaxzevria and 80% to 95% with Pfizer-BioNTech Comirnaty and Moderna Spikevax (3, 4) Vaccine effectiveness is generally slightly higher in younger compared to older age groups. With both Vaxzevria and Comirnaty, there is evidence of waning of protection over time, most notably among older adults. There is not yet enough follow-up with Spikevax to assess waning (Figure 1, 3).

Data (based primarily on the Alpha variant) suggest that in most clinical risk groups, immune response to vaccination is maintained and high levels of VE are seen with both the Pfizer and AstraZeneca vaccines. Reduced antibody response and vaccine effectiveness were seen after 1 dose of vaccine among the immunosuppressed group, however, after a second dose the reduction in vaccine effectiveness is smaller (5).

Analyses by dosing interval suggest that immune response to vaccination and vaccine effectiveness against symptomatic disease improves with a longer (greater than 6 week interval) compared to a shorter interval of 3 to 4 weeks (Figure 1, 6, 3).

Figure 1. Vaccine effectiveness against Delta symptomatic disease among individuals aged over 16, with 2 doses of Vaxzevria (AZ), Comirnaty (PF) or Spikevax (MD) in England and 95% confidence intervals

UK HSA_1

Effectiveness against hospitalisation

Several studies have estimated vaccine effectiveness against hospitalisation in older ages, all of which indicate higher levels of protection against hospitalisation with all vaccines against the Alpha variant (7, 8, 9, 10). Effectiveness against hospitalisation of over 90% is also observed with the Delta variant with all 3 vaccines (Figure 2, 3). In most groups there is relatively limited waning of protection against hospitalisation over a period of at least 5 months after the second dose. Greater waning appears to occur among those in clinical risk groups (Figure 2, 3).

Figure 2. Vaccine effectiveness against Delta hospitalisation among individuals aged over 16, with 2 doses of Vaxzevria (AZ), Comirnaty (PF) or Spikevax (MD) in England and 95% confidence intervals

UK HSA_2

Effectiveness against mortality

High levels of protection (over 90%) are also seen against mortality with all 3 vaccines and against both the Alpha and Delta variants (Figure 3, 7, 11, 3). Relatively limited waning of protection against mortality is seen over a period of at least 5 months.

Figure 3. Vaccine effectiveness against Delta death among individuals aged over 16, with 2 doses of Vaxzevria (AZ), Comirnaty (PF) or Spikevax (MD) in England and 95% confidence intervals

UK HSA_3

Effectiveness against infection

Although individuals may not develop symptoms of COVID-19 after vaccination, it is possible that they could still be infected with the virus and could transmit to others. Understanding how effective vaccines are at preventing infection is therefore important to predict the likely impact of the vaccination programme on the wider population. In order to estimate vaccine effectiveness against infection, repeat asymptomatic testing of a defined cohort of individuals is required. Studies have now reported on vaccine effectiveness against infection in healthcare workers, care home residents and the general population (12, 13, 14, 15). With the delta variant, vaccine effectiveness against infection has been estimated at around 65% with Vaxzevria and 80% with Comirnaty (4).

Vir: UK Health Security Agency, »COVID-19 vaccine surveillance report (week 45)«

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