Experts share essential updates on COVID-19 vaccines

SARS-CoV-2 continues to evolve into newer variants. Post-Delta, these variants are generally more highly transmissible and immune-evasive, although not more virulent, said Dr Gregory Poland, Mary Lowell Leary Emeritus Professor of Medicine and director of Mayo Vaccine Research Group, Mayo Clinic in Rochester, Minnesota, US, at IDWeek 2023.

“The currently circulating variants are Omicron sublineage. The XBB.1.5 monovalent vaccine offers some level of protection. However, we need SARS-CoV-2 monoclonal antibodies (mAbs) and improved antivirals,” he pointed out.

By now, most populations already developed hybrid immunity from previous infection and vaccination. Asymptomatic mild-to-moderate cases have been increasing as the number of severe cases decreases. “COVID-19 vaccination reduces post-COVID-19 conditions compared with no vaccination among individuals with SARS-CoV-2 infection, but it is projected that weekly hospitalizations would surge again during winter and would stay within last year’s range,” said Poland.

Recommendations for use of COVID-19 vaccines

The US Centers for Disease Control and Prevention recommends COVID-19 vaccination for everyone 6 months and older to protect against the potentially serious outcomes of COVID-19 illness, said Dr Flor Munoz, medical director, Transplant Infectious Diseases, Texas Children’s Hospital in Houston Texas, US. “Currently, there is no approved COVID-19 vaccine for infants younger than 6 months.”

Two types of COVID-19 vaccines are available in the US – the updated mRNA vaccines (2023-2024 Formula) by Moderna and Pfizer-BioNTech and the protein subunit vaccine (Novavax, Adjuvanted for ages ≥12 years). All three have been updated to a monovalent vaccine to target the Omicron XBB.1.5 sublineage. The original monovalent and bivalent (BA.4/BA.5) should no longer be used.

Vaccination guidance for updated mRNA vaccines

For unvaccinated infants and children (ages 6 months to 4 years), 2 doses of the updated Moderna vaccine or 3 doses of the updated Pfizer-BioNTech vaccine are recommended. Those previously vaccinated with 1 or more doses of any mRNA vaccine could get 1 or 2 doses of homologous updated mRNA vaccine based on the manufacturer’s recommendation. Those who have completed their primary vaccine series can receive 1 dose of the updated Moderna or Pfizer/BioNTech vaccine.

Unvaccinated individuals (≥5 years of age) and those previously vaccinated with 1 or more doses of any mRNA vaccine can receive 1 dose of the updated Moderna or Pfizer-BioNTech vaccine.

“Previously vaccinated individuals only need one dose of any updated mRNA vaccine to stay up to date with their vaccination schedule,” said Munoz.  People who recently had COVID-19 infection may need to consider delaying their vaccination by 3 months.

Those 12 years and older previously vaccinated with any COVID-19 vaccine (and have not received an updated mRNA COVID-19 vaccine) may opt for a single dose of Novavax COVID-19, Adjuvanted vaccine. Unvaccinated individuals require 2 doses.

Children and pregnant women

One of the questions Munoz addressed during the talk was whether there is a need to vaccinate children. According to CDC data, paediatric COVID-19 mortality is higher than for influenza. Widespread vaccination efforts have helped lower the death toll from flu, but children remain largely unvaccinated against COVID-19, she added.

As of May 2023, 56 percent of children aged 6 months to 17 years in the US have not received a first dose of the COVID-19 vaccine. “Myocarditis has been a concern, but there are no specific data to support it. The risk remains very low in paediatric population,” she said. “Risk-benefit assessments showed we need to vaccinate.”

Similarly, vaccination coverage among pregnant women remains low, according to an internet panel survey. Only 58.7 percent of pregnant women had completed their primary vaccine series and only 27.3 percent had received the bivalent booster. [MMWR Morb Mortal Wkly Rep 2023;72:1065-1071]

Munoz said COVID-19 vaccination in pregnancy is safe and immunogenic as in the nonpregnant population. “Pregnancy is not a contraindication to vaccination. There are no increased risks of miscarriage, stillbirth, or foetal/neonatal complications,” she added. “COVID-19 vaccines (mostly mRNA vaccines) are safe and effective for pregnant women and may be protective for their infants.” [N Engl J Med 2022;387:109-119]

The CDC in fact recommends primary and booster vaccination with COVID-19 vaccines for pregnant women. Booster vaccination during pregnancy results in higher antibody titres for mothers and their infants at birth. [IDWeek 2023, poster 116] This is also supported by the WHO Strategic Advisory Group of Experts on Immunization. [https://www.who.int/news/item/28-03-2023-sage-updates-covid-19-vaccination-guidance]

Immunocompromised population

Munoz said immunocompromised patients have different responses to vaccination. Some groups have lower antibody responses after repeated vaccination than others. Studies have shown the low immunogenicity of COVID-19 vaccines in solid organ transplant recipients and patients with haematological malignancy. [Clin Microbiol Infect 2022;28:163-172]

“So, people who are severely immunocompromised need to have different regimens,” she added. “We need studies that are powered to evaluate the effectiveness of updated COVID-19 vaccines in immunocompromised individuals.”

Vaccine guidance for moderately or severely immunocompromised

For unvaccinated infants and children (ages 6 months to 4 years), 3 doses of the homologous updated mRNA vaccine are recommended, said Munoz. “Those who completed 3 or more mRNA vaccine doses can be given a single dose of the homologous updated mRNA vaccine. Some may require additional doses.”

Similarly for unvaccinated children 5–11 years of age,  3 doses of the homologous updated mRNA vaccine are recommended. Those who completed 3 or more mRNA vaccine doses can receive one dose of the updated mRNA vaccine ≥2 months after the last recommended updated mRNA vaccine dose, she said.

“For those 12 years and older, we have the option to administer the updated mRNA vaccines or the protein-based vaccine. Doses are based on vaccination history,” Munoz added.

 No age group is safe

Both experts said there is no age group that is safe or exempt from the risk of infection, hospitalization, complications, or death due to COVID-19.

“We can only personalize the choice of vaccines [mRNA vs protein subunit].  There are no authorized mAbs currently available in the US. Finally, antivirals remain an option for individuals at high risk for complications.”