31st July 2023

Antiviral drugs and vaccines

Antivirals

There are relatively few antivirals available in comparison to antibiotics. One of the most common antivirals prescribed in clinical medicine is aciclovir – which is effective against herpes simplex virus and varicella zoster virus (the cause of shingles). Aciclovir and the related agents famciclovir and valaciclovir work through being phosphorylated by viral tyrosine kinase, resulting in early chain termination.

Antiretrovirals

HIV antiretroviral medications are numerous. HIV treatment is based on the principle of utilising multiple methods of attack on the virus simultaneously, known as highly active antiretroviral therapy (HAART). These drugs have revolutionised HIV treatment, making it a manageable, chronic illness. More information can be found in the HIV and Infections in Immunocompromised Hosts topic.

Vaccines

Multiple viruses now have effective vaccines against them. These vaccines can be classified by type. Classical types include live attenuated, toxoid, conjugate, and inactivated vaccines. More recent times have seen the advent of mRNA vaccines, which use the host’s genome to build the proteins that then mount a humoral immune response. Many of the new vaccines against COVID-19 are mRNA vaccines.

Some common vaccines are summarised by type in the table below.

Table 1: Examples of viral vaccines by type

Live attenuated vaccines should be avoided in the immunosuppressed. A full UK vaccine schedule can be found on the NHS website and is linked in the References section here.

Influenza antivirals and vaccines

The 2009 swine flu pandemic, caused by the H1N1 influenza virus, led to a rise in the use of oseltamivir (Tamiflu) and, less so, zanamivir (Relenza). These drugs are neuraminidase inhibitors, which block the binding of the neuraminidase antigen of the influenza virus to sialic acid receptors in the lung.

However, there is little evidence that oseltamivir prevents the complications of influenza; although it can help people recover from the illness more quickly. The evidence base for zanamivir is also weak, but it is regularly used to treat influenza A and B infections.

Influenza vaccines are adjusted each year, depending on the seasonal variants that have become dominant worldwide, which is why viral surveillance is so important. Influenza A and influenza B are the most common strains of the virus, and the vaccine is based around these. Most influenza vaccines contain traces of eggs, which is important to know for allergy purposes.